1. Field of the Invention
This invention relates generally to telecommunications systems, and, more particularly, to wireless telecommunication systems.
2. Description of the Related Art
The transmission power used to transmit symbols over an air interface, e.g. the air interface between a mobile unit and a base station in a wireless telecommunication system, is typically determined by balancing competing constraints. For example, increasing the transmission power may reduce a bit error rate associated with transmissions over the air interface. However, increasing the transmission power may also increase system interference between mobile units and/or base stations. Increasing the transmission power of a transmitter in a mobile unit may also reduce the operational lifetime of a battery in the mobile unit. Thus, the transmission power may be selected to balance the competing desires for a low bit error rate, low system interference, and long battery life.
The optimal transmission power typically varies over time. For example, the transmission power of a transmitter in a mobile unit and/or a base station may be continually increased to maintain an acceptable bit error rate as the mobile unit moves away from the base station, even though this may result in reduced battery life and/or increased system interference. Thus, closed loop power control systems may be used to control the transmission power of transmitters in wireless telecommunication systems. In a typical closed loop power control system, such as may be implemented in wireless telecommunications systems that operate in accordance with CDMA 2000 and/or UMTS protocols, feedback information is sent from a receiver to a transmitter at regular intervals. For example, the transmission power associated with slots in a frame may be controlled using a single power control bit that may be transmitted once per slot. The power control bit may instruct the transmitter to either reduce or increase the transmitted power for the next slot, depending upon a signal-to-noise ratio associated with a received signal, such as a pilot or traffic signal.
Coded transmission using closed loop power control may use more power than is needed to achieve the desired performance. The inefficiencies in the closed loop power control system may be caused by temporal channel variations in wireless telecommunication systems, insufficient granularity and/or step-size in the allowable levels of transmitted power, latencies in the power control loop, and the like. Consequently, closed loop power control may result in unnecessarily large system interference and reduced battery life.
The present invention is directed to addressing the effects of one or more of the problems set forth above.